Apparatus and method for recognizing subject motion using a camera

ABSTRACT

A method and an apparatus are provided for displaying pictures according to hand motion inputs. An application is executed for displaying a picture from among a sequence of pictures on a display. Groups of skin color blocks corresponding to a hand are detected from among image frames output from a camera. A motion is detected among the groups of skin color blocks. Direction information is obtained on the detected motion. The application is controlled to display a previous picture or a next picture in the sequence of pictures on the display according to the direction information.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 12/837,111, filed on Jul. 15, 2010, which claimspriority under 35 U.S.C. §119(a) to a Korean Patent Application filed inthe Korean Intellectual Property Office on Jul. 17, 2009 and assignedSerial No. 10-2009-0065434, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method fordetecting a subject's motions in captured images, and more particularly,to an apparatus and method for recognizing or detecting a user's handmotions in image frames received from a mobile camera, i.e., a cameraembedded in a mobile terminal.

2. Description of the Related Art

Mobile terminals (also known as mobile communication terminals orportable terminals), which were originally developed for voice calls,have evolved into devices that provide many different types of servicesto users. For example, more recently developed mobile terminals alsoprovide data services such as text messaging, photo and video services,and mobile banking service. Users of mobile terminals with a camera maycapture a variety of images with the camera. The mobile terminal with acamera may recognize shapes or patterns in the images, and control anoperation of a specific application based on the shape or patternrecognition results.

A conventional hand shape recognition method using a mobile camerapredefines recognizable hand shapes or hand patterns, and detects handshapes in images captured by the camera. More specifically, the mobileterminal searches a database in a memory for a predefined hand shapethat best corresponds with the detected hand shape, and triggers anevent associated with the search results. Commonly, the conventionalhand shape recognition method defines various hand shapes, anddiversifies the types of events corresponding to the defined handshapes.

The conventional hand shape recognition method predefines diverse handshapes corresponding to input signals, compares a hand shape in thecurrent input image with pre-learned or stored hand shapes, andinitiates an event based on the comparison results.

However, for mobile camera-based hand shape recognition applications, itis important to generate hand shape-triggered events that are robust tochanges in the use environment. In the conventional hand shaperecognition method, a database for hand shape learning and recognitionhas been implemented under the assumption that in any environment, thebackground color is not similar to the skin color and part of user'sbody, like the face, are not covered. Consequently, disturbing factorssuch as a change in lighting or scale, rotational displacement,background color, or covering, may significantly degrade recognitionperformance. Additionally, a task such as hand shape recognition demandssignificant computing resources that are necessarily limited in themobile environment.

SUMMARY OF THE INVENTION

The present invention is designed to address at least the aforementionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, aspects of the present invention provide ahand motion-based input method and a hand motion recognition apparatusand method, which are robust to various disturbing factors and high inspeed, and can be applied to a variety of mobile applications. This maybe accomplished by considering only motion characteristics of a targetclose in color to the skin in a way, which is robust to diversedisturbing factors like the lighting and scale without separatelydetecting hand shapes.

In accordance with one aspect of the present invention, a method isprovided for displaying pictures according to hand motion inputs. Anapplication is executed for displaying a picture from among a sequenceof pictures on a display. Groups of skin color blocks corresponding to ahand are detected from among image frames output from a camera. A motionis detected among the groups of skin color blocks. Direction informationis obtained on the detected motion. The application is controlled todisplay a previous picture or a next picture in the sequence of pictureson the display according to the direction information.

In accordance with another aspect of the present invention, an apparatusis provided for displaying pictures according to hand motion inputs. Theapparatus includes a display, and a memory for storing a sequence ofpictures. The apparatus also includes a controller configured to:execute an application for displaying a picture from among the sequenceof pictures on the display; detect, from among image frames output froma camera, groups of skin color blocks corresponding to a hand; detect amotion among the groups of skin color blocks; obtaining directioninformation on the detected motion; and control the application todisplay a previous picture or a next picture in the sequence of pictureson the display according to the direction information.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of certainembodiments of the present invention will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram schematically illustrating a mobile terminalwith a hand motion recognizer for recognizing hand motions in inputimages according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating a detailed structure of a handmotion recognizer as illustrated in FIG. 1;

FIG. 3 is a flowchart illustrating a method for recognizing hand motionsin input images according to an embodiment of the present invention;

FIGS. 4A to 4D are diagrams illustrating steps of estimating directionsof hand motions;

FIGS. 5A to 6B are diagrams illustrating steps of determining strengthsof momentums; and

FIGS. 7A to 8B are diagrams illustrating steps of allocating events.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

The present invention provides high-speed hand motion recognition andhand motion-based input method, which is robust to various disturbingfactors, and can be applied to various mobile applications, byconsidering only motion characteristics of a target (i.e., a subject oran object in an image) close in color to the skin, which are robust to avariety of disturbing factors like lighting and scale, by recognizinghand motions (basically, a subject's motions appearing in images)instead of hand shapes in captured images. The term “hand motion-basedinput” refers to using hand motion recognition results as userinterfaces, which may be applied to various applications such as to viewphotos or play games.

FIG. 1 is a block diagram, which schematically illustrates a mobileterminal including a hand motion recognizer for recognizing hand motionsin input images according to an embodiment of the present invention.

Referring to FIG. 1, a mobile terminal 100 includes a camera 110, anImage Signal Processor (ISP) 120, a display 130, a wirelesscommunication unit 140, a hand motion recognizer 200, a controller 150,and a memory unit 160. Although only an overview of the mobile terminal100 is illustrated in FIG. 1, the mobile terminal 100 may furtherinclude a speaker, a microphone, and a user interface device like akeypad.

The camera 110 captures an image of a subject, and detects the capturedimage in an electrical signal. For this purpose, the camera 110, thoughnot shown here, may include a lens system having at least one lens toform an image of a subject, and an image sensor, such as aCharge-Coupled Device (CCD) image sensor and/or a ComplementaryMetal-Oxide Semiconductor (C-MOS) image sensor, for converting the imageformed on the lens system to an electrical signal.

The ISP 120, under the control of the controller 150, processes imagesignals received from the camera 110 or images stored in the memory unit160 on a frame-by-frame basis, and outputs image frames that have beenconverted according to screen characteristics (size, quality,resolution, etc.) of the display 130.

The display 130 displays image frames received from the ISP 120 on ascreen. A Liquid Crystal Display (LCD), a touch screen, or the like maybe used as the display 130. The touch screen displays images under thecontrol of the controller 150. If a user input, such as a finger or astylus pen, comes in contact with its surface, the touch screengenerates a key contact interrupt and outputs user input informationincluding input coordinates and input status to the controller 150.

The wireless communication unit 140 receives wireless downlink signalsover the air via an antenna, and outputs downlink data obtained bydemodulating the wireless downlink signals, to the controller 150. Also,the wireless communication unit 140 generates wireless uplink signals bymodulating uplink data received from the controller 150, and wirelesslytransmits the generated wireless uplink signals into the air via theantenna. The modulation and demodulation may be carried out using CodeDivision Multiple Access (CDMA), and may also be performed usingFrequency Division Multiplexing (FDM) or Time Division Multiplexing(TDM).

The hand motion recognizer 200 recognizes hand motions from image framesreceived from the ISP 120, and outputs the recognition results to thecontroller 150.

The memory unit 160 may store applications with various functions suchas games, images for offering Graphical User Interfaces (GUIs)associated with the applications, databases regarding user informationand documents, and background images (menu screens, idle screen, etc.)or other programs for operating the mobile terminal 100.

The controller 150 runs an application corresponding to user inputinformation, and the application performs a program operationcorresponding to the user input information. The user inputs may includenormal inputs made using keypads, touch screens, etc., and camera-basedhand motion inputs. For example, if a user moves his hand toward thecamera from side to side while a photo album application is running, thephoto album application may replace the current photo displayed on thedisplay 130 with the next photo. Such an action might trigger a “FlipPhoto Album” event in reply to the hand motion causing the eventprocessing result (i.e., flipping to the next photo) to be displayed onthe display 130.

FIG. 2 is a block diagram illustrating a hand motion recognizer 200, andFIG. 3 is a flowchart illustrating a method for recognizing hand motionsin input images according to an embodiment of the present invention.

The hand motion recognizer 200 includes a skin color detector 210, amotion block detector 220, a momentum & direction determiner 230, and anevent allocator 240. The hand motion recognition method includes amotion block extraction step S110, a motion center estimation step S120,an inter-motion frame speed & momentum estimation step S130, a momentumcomparison step S140, an input direction and strength estimation stepS160, and an event allocation step S170.

In the motion block extraction step S110, the skin color detector 210detects skin color blocks (or motion candidate blocks) corresponding toa hand in image frames received from the ISP 120, and the motion blockdetector 220 detects motion blocks among the skin color blocks.

The skin color detector 210 receives an image frame from the ISP 120,and splits the image frame into blocks each having a predeterminednumber of pixels in order to reduce noises and computation. This imagesplitting step may be performed on the entire image frame, or on an areaof interest in the image frame displayed on the display 130. The area ofinterest may be determined by the user or the controller 150. Also, thearea of interest may be automatically set according to, for example, adefault value stored in the memory unit 160. The image splitting step isa virtual step, and the image frame is split into, for example, N*Mblocks and processed in the hand motion recognizer 200 on ablock-by-block basis. For example, each of the blocks may have a size of8*8 or 16*16 pixels.

The skin color detector 210 detects pixels (hereinafter, skin colorpixels) close in color to the skin among the pixels included in eachblock, and determines a certain block as a skin color block if thenumber of the detected skin color pixels is greater than or equal to apredetermined ratio (e.g., 60 to 80%) of the total number of pixels inthe block.

For example, when the image frame is expressed in an YCrCb format (orcolor model), the skin color detector 210 can determine skin colorpixels, using Equation (1) below.Cb>(76−SkinColorMargin)&&Cb<(128+SkinColorMargin)&&Cr>(132−SkinColorMargin)&&Cr<(174+SkinColorMargin)  (1)

A SkinColorMargin value may be set to 10 so that it may include a colorvalue similar to that of the skin color, and the specific figures inEquation (1) are given by way of example.

Thus, the skin color detector 210 determines whether or not a colorvalue of each pixel satisfies Equation (1) or if it falls within athreshold range.

The motion block detector 220 detects motion pixels among the pixelsincluded in each skin color block, and determines the skin color blockas a motion block if the number of the detected motion pixels is greaterthan or equal to a predetermined ratio of the total number of pixels inthe block. This motion block detection step is performed on the currentimage frame and the previous image frame on the basis of the currentimage frame at a sampling time of each image frame. The motion blockdetector 220 compares each pixel value (or a brightness value) of a skincolor block in the current image frame with a pixel value of the samepixel in the previous image frame and determines the pixel to be amotion pixel if the difference between the pixel values is greater thanor equal to a predetermined pixel threshold (e.g., 10˜30 in the YCrCbformat). The motion block detector 220 determines a pertinent skin colorblock as a motion block if the number of motion pixels included in eachskin color block is greater than or equal to a predetermined blockthreshold or a predetermined ratio (e.g., 60 to 80%) of the total numberof pixels in the skin color block.

The reason for detecting motion blocks from among the skin color blocksin this embodiment (instead of simply estimating motions of the skincolor blocks) is to extract only the target having a relatively largemotion because the image frame may contain the user's face in additionto his or her moving hand. Therefore, the motion block estimation (ormatching) step described above is optional depending on the useenvironment of the present invention, or the features of theapplication.

In addition, the skin color blocks are detected in order to exclude amotion of the background in the image frame. Thus, the above-describedskin color block detection step is also optional depending on the useenvironment of the present invention, or the features of theapplication.

While a user's hand is described above as an example of the targetsubjected to motion estimation, motions of other targets, like a face,may also be estimated depending on the input method of the application.

In the motion center estimation step S120, the momentum & directiondeterminer 230 estimates the central point (or motion center) for allmotion blocks in each of the image frames. Such a central point may bedetermined as the center of the whole distribution area of the motionblocks, the center of an area where the motion blocks are crowded, orthe center given by a combination of both methods. For example, everyarea may be given a different weight depending on the density of motionblocks.

In the inter-frame speed and momentum estimation step S130, the momentum& direction determiner 230 calculates the speed and the momentum of ahand motion based on a distance between the motion centers of thecurrent and previous image frames. For example, the hand motionrecognition may be achieved by simply calculating the distance betweenthe motion centers of the current and previous image frames. That is, aspeed of the hand motion is expressed in the distance between the motioncenters as described below, and in the case of a simple application,hand motion inputting may be completed by simply estimating the handmotion's speed. Estimating the momentum, strength, direction, and handmotion speed offers a variety of events according to the state of thehand motion.

If coordinates of the motion centers of the current and previous imageframes are defined as {x1, y1} and {x2, y2}, respectively, then a speedof the hand motion can be written as Equation (2) below.Speed=sqrt(x1−x2)*(x1−x2)+(y1−y2)*(y1−y2))  (2)

In Equation (2), sqrt( ) represents a square root function, and thespeed is expressed in a distance between motion centers. In thiscontext, a time difference between image frames being input to the handmotion recognizer 200, i.e., a sampling interval between the imageframes, is constant, and the speed and momentum of the hand motion aremeaningful as relative values for comparison, so the sampling intervalis omitted in Equation (2). Thus, the “speed” of the hand motioncorresponds to the distance of the hand motion, or the magnitude of amotion vector.

A moment used to calculate a momentum of the hand motion can be writtenas Equation (3) below.Moment=Max(N _(MB) _(—) _(current) ,N _(MB) _(—) _(Previous))  (3)

In Equation (3), N_(MB) _(—) _(current) represents the number of motionblocks in the current image frame, N_(MB) _(—) _(Previous) representsthe number of motion blocks in the previous image frame, and Max( )represents a function for calculating the maximum value among factors.

Although the maximum value function Max( ) is used above to calculatethe momentum of the hand motion, an average function may be used in thealternative.

The momentum P calculated using the speed and moment of the hand motioncan be written as Equation (4) below.P(momentum)=Moment*Speed  (4)

In the momentum comparison step S140, the momentum & directiondeterminer 230 compares the momentum of the hand motion with apredetermined momentum threshold. If the momentum is less than or equalto the threshold, the momentum & direction determiner 230 does notperform the input's direction & strength estimation step in step S150,determining that the hand motion is invalid. If the momentum exceeds thethreshold, the momentum & direction determiner 230 performs the inputdirection and strength estimation step S160. The mobile terminal woulduse the square root value (or an approximation thereof) to determineSpeed, or the value of Speed squared may be substituted increasecomputational efficiency.

While the description above considers the number of motion blocks andthe hand motion's speed in the momentum comparison step S140 toaccurately determine the presence/absence of a hand motion input, thiscomparison step may be optionally replaced by comparing only the speed.

In the input direction and strength estimation step S160, the momentum &direction determiner 230 estimates direction and strength of the handmotion. For example, for (x1−x2)>0, the momentum & direction determiner230 may determine that the hand motion was made in the right direction(or +x direction), while for (x1−x2)<0, the momentum & directiondeterminer 230 may determine that the hand motion was made in the leftdirection (or −x direction). A decision on the up-down direction (y-axisdirection) may be made in the same manner. In addition, for(x1−x2)/(y1−y2)>1, the momentum & direction determiner 230 may determinethe direction on the x-axis as stated above, determining that the handmotion was made in the left-right direction (x-axis direction), whilefor (x1−x2)/(y1−y2)<1, the momentum & direction determiner 230 maydetermine the direction on the y-axis as stated above, determining thatthe hand motion was made in the up-down direction (y-axis direction).

FIGS. 4A to 4D illustrate a process of estimating hand motiondirections. In FIGS. 4A to 4D, the arrows indicate the directions ofhand motions, and motion blocks 610 to 640 are estimated based on thehand motions. FIG. 4A illustrates an image frame of a user making anupward hand motion, and the motion blocks 610 corresponding thereto.FIG. 4B illustrates an image frame of a user making a downward handmotion, and the motion blocks 620 corresponding thereto. FIG. 4Cillustrates an image frame of a user making a leftward hand motion, andthe motion blocks 630 corresponding thereto. FIG. 4D illustrates animage frame of a user making a rightward hand motion, and the motionblocks 640 corresponding thereto. As illustrated in FIGS. 4A to 4D, agroup of motion blocks lean toward the direction in which the user madethe hand motion, making it possible to estimate the direction of thehand motion by identifying the center of the motion block group.

The momentum & direction determiner 230 estimates the strength (ormagnitude) of the momentum by comparing the momentum with apredetermined threshold range. For example, if the strength of themomentum is greater than the threshold and less than 10 in the momentumcomparison step S140, the strength is determined as level-1 strength. Ifthe strength of the moment is greater than or equal to 10 and less than20, the strength is determined as level-2 strength. If the strength ofthe momentum is greater than or equal to 20 (another thresholdcorresponding to the top limit may be set), the strength is determinedas level-3 strength.

FIGS. 5A to 6B are diagrams illustrating steps of determining strengthsof momentums. In FIGS. 5A to 6B, the arrows in the image framesrepresent the directions and strengths of the hand motions. FIGS. 5A and5B illustrate a situation where level-1 strength occurs as the usermakes a hand motion from left to right at low speed. It is noted that adifference between the center of a motion block group 310 in theprevious image frame illustrated in FIG. 5A and the center of a motionblock group 320 in the current image frame illustrated in FIG. 5B is notso large.

FIGS. 6A and 6B illustrates a situation where level-3 strength occurs asthe user makes a hand motion from left to right at high speed. It can beappreciated that a difference between the center of a motion block group410 in the previous image frame illustrated in FIG. 6A and the center ofa motion block group 420 in the current image frame illustrated in FIG.6B is relatively large.

In the event allocation step S170, the event allocator 240 generates anevent allocated to the direction and strength of the momentum,determined in the input direction and strength estimation step S160. Forexample, this event may signal a photo album application to “flip” the“pages” of an album. In this case, the controller 150 may display theexecution results of the Flip Photo Album event, i.e., the next photo,on the display 130.

FIGS. 7A to 8B are diagrams illustrating steps of allocating events.FIGS. 7A to 7D illustrate four successive image frames. In FIGS. 7A to7D, the arrows indicate the directions of hand motions, and motionblocks 510 to 540 are estimated based on the hand motions. The eventallocator 240 generates a Flip Photo Album event (i.e., a Page Up event)in reply to the leftward hand motion appearing in the image frames, andthe execution results of the Flip Photo Album event are illustrated inFIGS. 8A and 8B. That is, the previous photo illustrated in FIG. 8A isreplaced with the current photo illustrated in FIG. 8B. If the usermakes a rightward hand motion, a Flip Photo Album event (i.e., a PageDown event) is generated to replace the photos in the oppositedirection. For example, in a cartoon application, if a Page Up eventoccurs, the page is flipped from 10 to 11, whereas if a Page Down eventoccurs, the page is flipped from 10 to 9.

As is apparent from the foregoing description, in order to run mobileapplications depending on the most intuitive hand motions, in accordancewith an embodiment of the present invention image blocks similar incolor to the skin are set as interested motion candidate blocks, themotion blocks are extracted from the interested motion candidate blocksusing the motion block detector, the center of the motion blocks iscalculated, and the speed and momentum of the hand motions are estimatedbased on a difference between the centers of motion blocks in differentmotion frames and the number of motion blocks. The estimated data may beapplied to a variety of mobile applications. For example, the estimateddata can be applied to a mobile camera-based User Interface (UI) forviewing photos that is responsive to hand motions. In addition, theembodiments of the present invention can preset event timing, sense theposition where a hand motion occurs at the cycle of the event timing,and allocate an event based thereon, thereby supporting hand-faceguessing games like the Korean game Cham-Cham-Cham. The presentinvention could also be used for Olympic-type games (broad jump, hurdlerace, etc.) in which events are generated depending upon the frequencyand timing of hand motions, and other sports games (tennis, ping-pong,etc.) in which events are generated depending on the strength and timingof hand motions. Accordingly, the embodiments of the present inventioncan be applied to a variety of games and UIs that detect and determineup/down/left/right directions.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method for displaying pictures according tohand motion inputs, comprising: executing an application for displayinga picture from among a sequence of pictures stored in a memory on adisplay; detecting, from a current image frame output from a camera,skin color blocks corresponding to a hand; detecting a group of motionblocks from the skin color blocks; detecting a motion of the group ofmotion blocks; obtaining momentum information on the detected motion;and controlling the application to display a previous picture or a nextpicture in the sequence of pictures on the display according to themomentum information, wherein the skin color blocks are detected by:detecting skin color pixels from each of a plurality of image blocksincluded in the current image frame, each of the skin color pixelshaving a color value falling within a first threshold range; anddetecting the skin color blocks from among the plurality of image blocksby comparing a number of the detected skin color pixels in each of theplurality of image blocks with a first threshold, and wherein the groupof motion blocks are detected by: detecting motion pixels from each ofthe skin color blocks, a difference between a pixel value of each of themotion pixels in the current image frame and a pixel value of each ofthe motion pixels in a previous image frame output from the camerafalling within a second threshold range; and detecting the group ofmotion blocks from among the skin color blocks by comparing a number ofthe detected motion pixels in each of the skin color blocks with aseconded threshold, and wherein the momentum information is obtained bycalculating momentum based upon the number of motion blocks and adistance between motion pixels in the current image frame and motionpixels in a previous image frame.
 2. The method of claim 1, wherein theprevious picture in the sequence of pictures is displayed on the displaywhen a direction of the motion is a first direction, and wherein thenext picture in the sequence of pictures is displayed on the displaywhen the direction of the motion is a second direction opposite to thefirst direction.
 3. The method of claim 1, further comprising: obtainingspeed information on the detected motion, wherein a current picture inthe sequence of pictures is switched with the previous picture or thenext picture according to the momentum information and the speedinformation.
 4. The method of claim 1, further comprising: obtainingspeed information on the detected motion; and determining, from among aplurality of speed levels, a speed level corresponding to the speedinformation, wherein a current picture in the sequence of pictures isswitched with the previous picture or the next picture according to themomentum information and the determined speed level.
 5. An apparatus fordisplaying pictures according to hand motion inputs, comprising: adisplay; a memory for storing a sequence of pictures; a controllerconfigured to: execute an application for displaying a picture fromamong the sequence of pictures on the display; detect, from a currentimage frame output from a camera, skin color blocks corresponding to ahand; detect a group of motion blocks from the skin color blocks; detecta motion of the group of motion blocks; obtaining momentum informationon the detected motion; and control the application to display aprevious picture or a next picture in the sequence of pictures on thedisplay according to the momentum information, wherein the controller isconfigured to detect the skin color blocks by: detecting skin colorpixels from each of a plurality of image blocks included in the currentimage frame, each of the skin color pixels having a color value fallingwithin a first threshold range; and detecting the skin color blocks fromamong the plurality of image blocks by comparing a number of thedetected skin color pixels in each of the plurality of image blocks witha first threshold, and wherein the controller is configured to detectthe group of motion blocks by: detecting motion pixels from each of theskin color blocks, a difference between a pixel value of each of themotion pixels in the current image frame and a pixel value of each ofthe motion pixels in a previous image frame output from the camerafalling within a second threshold range; and detecting the group ofmotion blocks from among the skin color blocks by comparing a number ofthe detected motion pixels in each of the skin color blocks with asecond threshold, wherein the momentum information is obtained bycalculating momentum based upon the number of motion blocks and adistance between motion pixels in the current image frame and motionpixels in a previous image frame.
 6. The apparatus of claim 5, whereinthe previous picture in the sequence of pictures is displayed on thedisplay when a direction of the motion is a first direction, and whereinthe next picture in the sequence of pictures is displayed on the displaywhen the direction of the motion is a second direction opposite to thefirst direction.
 7. The apparatus of claim 5, wherein the controller isconfigured to obtain speed information on the detected motion, wherein acurrent picture in the sequence of pictures is switched with theprevious picture or the next picture according to the momentuminformation and the speed information.
 8. The apparatus of claim 5,wherein the controller is configured to: obtain speed information on thedetected motion; and determine, from among a plurality of speed levels,a speed level corresponding to the speed information, wherein a currentpicture in the sequence of pictures is switched with the previouspicture or the next picture according to the momentum information andthe determined speed level.